Bicycle Fitting and Sizing

Serotta

Serotta has been a leader in bicycle fit for quite a while. The established the Serrotta Cycling Institute to further the goals of a better understanding of bike fit.

Fit Bikes

• Purely Custom/SICI
• Calfee Sizer Cycle
• Waterford Fitmaster
• Serotta Fit Bike
• San Giorgio Fig Jig
• Tiemeyer Cycles Position Cycle

My fit bike

I got myself one of the Calfee/Mikkelson Sizer Cycles. Fun!!! I also have a PowerTAP rear wheel for it to measure power gains in different postitions.

Goniometers

http://en.wikipedia.org/wiki/Goniometer

A goniometer is used to measure the angle of the knee as well as other joints on the body when doing a fit. The goniometers that are sold throught medical channels are just too short to get good results. You need between 18" and 24". I have found a couple of very good alternatives.

Quint Measuring Systems, Inc. P.O. Box 280, San Ramon, CA 94583 (800)745-5045 http://www.quintmeasuring.com/

• 24" True Angle Tool - Contractor Grade (Heavy-Duty)
• 18" True Angle Tool
• 4" Attachable Dial
• 7" Attachable Dial

I got the 24" version because it is more rugged and thicker.

Kits

• Retul, 3D computer anylisis
• Fit Kit
• Bikefitting.com
• Bike Fit Systems
• Accufit by Bill Boston

Local Fitters

• NorCal Cycling in Santa Rosa. $75. They do a pretty good job. Much better than the average bike shop in the bay area. This is where I send most people that need a basic fitting.
• Whole Athelete, San Anselmo, CA, $220-295
• Craig Upton of Performance Lab HC , $150
• PK Racing, in Fairfax. $450-500. Primarily pro road/tri experts. They are very expensive and I have no personal experience with them other than the fact that they are only 3 blocks from my house.
• Cycle Sport, in Oakland. $125
• AriaVelo, in Santa Rosa.
• HyperCat Racing, SF

or search Serotta by zip code

Links

• Ergo Bike Competition Bicycle Size/ Proportions Analysis By Edward C. Zimmermann
• Jack's Bikes - A fit kit walk through
• Cyclemetrics link page
• Pruitt
• Steve Hogg

A cool poster from Ritchey Logic: http://ritcheylogic.com/media/File/5022_FIT_LOGIC_POSTER_090909lowres.pdf

Some Traditional Numbers

Weight Distribution

Road:

• In drops decending: 45% Front / 55% Rear
• On tops climbing: 40% Front / 60% Rear
• On hoods, out of saddle, sprinting: 50% Front / 50% Rear

MTB:

For trail I prefer a setup that sets the rider as far back as possible while maintaining control on steepest climb without too much fussing.

Fox racing shox recomends 55% for X-Country, 65% for Freeride, and 70% for Downhill.

When designing a frame from scratch, wheel offset from BB along wheelbase can be used as a ballpark start.

• Road - 58.5%F/41.5%R
• Trailbike - 61%F/39%R
• MTB Race 60%F/40%R.

Cleat Position

"5. Make sure that the ball of your foot [centre of the first metatarsal joint] is in front of the pedal axle with the crank arm forward and horizontal. For a rough guide for shoe size metric 36 - 38, 7mm in front; 39 - 41, 8mm in front; 42 - 43, 9mm in front; 44 -45, 10mm in front. It is unlikely that your feet are bigger than that. Don't forget to move the right cleat further back again as outlined in point 3. I know that this is at variance with the commonly given advice but you will find as you try it that it works."

http://www.cyclefitcentre.com/pdf%20final%20docs/SHOE%20AND%20PEDAL%20ARTICLE%208_final.pdf

http://www.cyclingnews.com/fitness/?id=2004/letters07-26#Cleat

http://www.cyclingnews.com/fitness/?id=2004/letters10-11#Ball

Crank Length

39.5% of femur length.

L(mm) = 2.16% x I(mm)

http://www.polaris.net/palmk/crankset.html

"As a matter of fact, a large, persistent drop in cadence is usually a good indication that the crank is, in fact, too long."

2.10% for taller riders

Popular Guides Height Inseam Cranklength

under than 5' <=70 cm. 165

5' to 5'2" <=74 cm. 167.5

5'2" to 5'7" <=80 cm. 170

5'7" to 6' <=86 cm. 172.5

6' to 6'5" <=93 cm. 175

taller than 6'5" <=99 cm. 177.5 - 180.0

Traditional Recomendations Height Inseam Cranklength

under 5'7" 74 to 80 cm. 170

5'7" to 6' 81 to 86 cm. 172.5

Over 6' longer than 87 cm 175

http://www2.bsn.de/Cycling/cranks.html

18.5% from top of femur to floor.

Inseam:

• < 29 inches - 165 mm crank
• 29 - 32 inches - 170 mm crank
• 32 - 34 inches - 172.5 mm crank
• > 34 inches - 175 mm crank

Frame Size:

• 54 cm or less, 170 mm
• 55 - 58 cm, 172.5 mm
• 59 cm or greater, 175 mm

• Gonzalez and Hull, Bivariate optimization of pedaling rate and crank arm length. Journal of biomechanics 1988, vol. 21, no10, pp. 839-849

• Danny Too; Gerald E. Landwer, The effect of pedal crank arm length on joint angle and power production in upright cycle ergometry. Journal of Sports Sciences, Volume 18, Issue 3 March 2000 , pages 153 - 161

Knee Angle

30-35 Degrees. More bend conserves more energy, less bend for more power.

31-32 is optimum.

Saddle Height

• Inseam (with cycling shoes) x 0.883 = Top of the saddle to the center of the bottom bracket. (beware oversized feet using this)
• Inseam (with cycling shoes) x 1.09 = Pedal spindle to top of saddle with pedal parallel to seat tube.

• LeMond Method - Adjust the saddle to a distance equal to your PBH* x .883, measured from the top of saddle to the center of the bottom-bracket
• Petersen Method - Adjust the saddle to a distance equal to your PBH x .873, measured from the top of saddle to the center of the bottom-bracket
• Hamley Method - Adjust the saddle to a distance equal to your PBH x 1.09, measured from the top of saddle to the pedaling surface (with the crank at bottom-dead-center inline with the seat tube)
• Holmes Method - Adjust the saddle so your knee is bent 25-35 degrees with the ball of your foot on the pedal (with the crank at bottom-dead-center inline with the seat tube)

Trunk Angle

About 30-40 degrees from level. (45 at most)

Shoulder Angle

90-100 degrees.

Elbow Bend

15 degrees

Stem Length

• Shoulder angle 90 degrees +/- 5 degrees.
• When in drops, axle obscured by bars.
• With arms bent 15 degrees in drops, plumb line from nose bisects stem at bars.

Handlebar Height

• 1-2 inches below the saddle for small riders
• up to 4 inches for taller riders.